Antenna Simulation of a Circular Disc Monopole antenna

These days, printed antennas are in-creasingly becoming popular thanks to their low-profile and ease of fab-rication. However, they are limited to operate over a very narrow band-width. In this example, the anten-na is a printed circular monopole with an ultra wide band: We analyze and compare their simulated per-formances to the published results. The printed monopole antenna is in essence a substrate backed with a ground plane on one side and printed with a patch on the other. The open air around the antenna is included and truncated. In this study, we ex-ploited the symmetry of the model tolessen solving time consumption through the use of symmetry bound-ary conditions.

Figure 1: Circular Disc Monopole Antenna (3D SolidWorks view)

Description

Simulation

To simulate the behavior of this antenna, we create an antenna study, and specify the rel-evant frequency range at which the antenna operates. Here we use the “fast sweep” for frequency sweep type: The fast sweep greatly reduces the simulation time of an S-parame-ter study through the use of the reduced-or-der model. By solving the matrix equations of a single frequency, the reduced-order model is produced. Other surrounding frequencies in the band of interest are then solved using the reduced model instead of the full matrix solu-tion, allowing for a much faster trial and error period. In HFWorks 2012, the fast sweep op-tion has been further developed into the adap-tive fast sweep. This advanced feature which is exclusive to HFWorks, employs new expan-sion points whenever the error of the reduced order model exceeds a certain threshold. The only thing that the user needs to provide is themaximum number of expansion points. An ad-ditional option has also been added which al-lows the user to decide whether he wants the software to compute the field information or not. Of course if the fields are not computed the analysis would be much faster.

SOLIDS AND MATERIALS

In figure 1, we have shown the discretised model of the anten-na. As mentioned in thedescription of the model, the substrate of the antenna has on both of its sides two printed planes: theground and the patch. The air is included and conveniently truncated to show the radiation results.

Figure 2: Boundary conditions of the antenna

On the figure, we can spot the different boundary conditions; from the right we have the sym-metric PEM. The port is marked with red arrows pointing to two faces. The arrows in yellow show the PEC faces which are the two printed conductors of the an-tenna. The radiation boundaries are applied to the remaining air box faces.

Figure 3: Mesh of the half DR filter

MESHING

RESULTS

Since the antenna’s radiation sources lie in the port and the distribution and direction of E-field are partly defined by the form of PEC surfaces from both sides, the mesh has to focus more on these ports and PEC faces. Meshing these surfaces help the solver refine its precision on the eddy parts, and take their particular (if there is any) forms into account. There is always a compromise between accuracy, time consumption and meshing. Applying an over accurate mesh control may result in much time consumption and causes slow processors to be over loaded; this has no benefits but refining the degree of precision which at most cases appears to be irrelevant to task. On the other hand, meshing should re-spond to a certain threshold of accuracy which is sometimes warned by HFWorks, when the global size of the mesh element is bigger than some structure’s dimensions. Therefore, choosing the mesh element size is sometimes crucial to get good results

Various 3D and 2D plots are available to exploit, depending on the nature of the task and onwhich parameter the user is interested in. As we are deal-ing with an antenna simulation, plotting the radiation intensity along with the reflection coef-ficient sounds like an intuitive task.

As mentioned within the beginning of this report, HFWorks plots curves for electricalparameters on 2D plots as well as on smith charts. The latter is more suitable for matching issues: The antenna in this example is best matched at 5.5 GHz, with a return loss of 17.3 dB. The 3D plots for the antenna studies cover a wide range of parameters: we can view the electricfield distribution, its components in differ-ent coordinate systems, and parameters peculiar to antenna studies such as radia-tion and directivity

Figure 4: Variations of return loss (S11)

Figure 5: Electric field vector distribution (at 7 GHz)

On this figure, the radiated electric field along the Theta component is plotted on the plane Phi=0.

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